Perceptual order and the effect of vocalic context on fricative perception

This three-part study demonstrates that perceptual order can influence the integration of acoustic speech cues. In Experiment 1, the subjects labeled the [s] and [∫] in natural FV and VF syllables in which the frication was replaced with synthetic stimuli. Responses to these “hybrid” stimuli were influenced by cues in the vocalic segment as well as by the synthetic frication. However, the influence of the preceding vocalic cues was considerably weaker than was that of the following vocalic cues. Experiment 2 examined the acoustic bases for this asymmetry and consisted of analyses revealing that FV and VF syllables are similar in terms of the acoustic structures thought to underlie the vocalic context effects. Experiment 3 examined the perceptual bases for the asymmetry. A subset of the hybrid FV and VF stimuli were presented inreverse, such that the acoustic and perceptual bases for the asymmetry were pitted against each other in the listening task. The perceptual bases (i.e., the perceived order of the frication and vocalic cues) proved to be the determining factor. Current auditory processing models, such as backward recognition masking, preperceptual auditory storage, or models based on linguistic factors, do not adequately account for the observed asymmetries.     

Comparison of consonantal and vocalic cues in selective adaptation

The acoustic cues to the phonetic identity of diphthongs normally include both spectral quality and dynamic change. This fact was exploited in a series of selective adaptation experiments examining the possibility of mutual adaptive effects between these two types of acoustic cues. One continuum of syllables varying from [εi] to [εd] and another varying from [ε] to [εi] were synthesized; endpoint stimuli of both series used as adaptors caused identification boundaries to be shifted. Cross-series adaptation was also attempted on the [ε?εi] stimuli, using [?], [∞], and [ai]. Only [ai] proved effective as an adaptor, suggesting the mediation of a rather abstract auditory level of similarity. The results argue strongly against interpretations in terms of feature detectors, but appear compatible with an “auditory contrast” explanation, which might in turn be incorporated within adaptation level theory in the form recently discussed by Restle (1978). The cross-series results further suggest that selective adaptation might be used to quantify the perceptual distance between auditory cues in speech.     

The effect of segmental order on fricative labeling by children and adults

We examined whether children modify their perceptual weighting strategies for speech on the basis of the order of segments within a syllable, as adults do. To this end, fricative-vowel (FV) and vowel-fricative (VF) syllables were constructed with synthetic noises from an/[symbol: see text]/-to-/s/continuum combined with natural/a/and/u/portions with transitions appropriate for a preceding or a following /[symbol: see text]/or/s/. Stimuli were played in their original order to adults and children (ages of 7 and 5 years) in Experiment 1 and in reversed order in Experiment 2. The results for adults and, to a lesser extent, those for 7-year-olds replicated earlier results showing that adults assign different perceptual weights to acoustic properties, depending on segmental order. In contrast, results for 5-year-olds suggested that these listeners applied the same strategies during fricative labeling, regardless of segmental order. Thus, the flexibility to modify perceptual weighting strategies for speech according to segmental order apparently emerges with experience.     

Context effects in two-month-old infants' perception of labiodental/interdental fricative contrasts

We investigated 2-month-old infants' perception of a subset of highly confusable English fricatives. In Experiment 1, infants discriminated modified natural tokens of the voiceless fricative pair [fa]/[oa] but only when the syllables included their frication noises. They also discriminated the voiced pair [va]/[oa] both with and without fricative noises. These results parallel those found with adults by Carden, Levitt, Jusczyk, and Walley (1981). In Experiment 2 [f] and [o] noises were appended to [a], and the same [f] noise was appended to the previously indiscriminable fricationless versions of [fa] and [oa]. Infants discriminated both pairs of stimuli, indicating that (a) the frication is a sufficient cue for [fa]/[oa] discrimination and that (b) it provides a context for discriminating the [f] and [o] formant transitions. We conclude that infants' perception of labiodental/interdental fricative contrasts show evidence of context effects similar to those observed with adults.     

塞辅音范畴通达的时间进程：来自语境效应的证据

采用语境效应范式,以汉语听者为被试,在三个实验中考察了塞辅音声学信息和语音信息激活的时间进程。实验1语境刺激是/ta/、/ka/音节和/ta/、/ka/塞音段的声学模拟音,目标刺激是/ta/-/ka/对比连续体,结果发现,塞音声学信息激活没有产生语境效应。实验2语境刺激是/ta/、/ka/音节和/ta/、/ka/塞音段,结果发现塞音语音信息激活产生了显著的对比语境效应。实验3变化塞音段和目标刺激之间的间隔,系统考察塞音范畴通达的时间进程,结果发现,塞音知觉中听觉加工阶段向语音加工阶段的转变约发生于刺激加工后120 ms。实验结果揭示了塞辅音知觉中音位范畴通达的时间进程。     

Psychophysics of the McGurk and other audiovisual speech integration effects

When the auditory and visual components of spoken audiovisual nonsense syllables are mismatched, perceivers produce four different types of perceptual responses, auditory correct, visual correct, fusion (the so-called McGurk effect), and combination (i.e., two consonants are reported). Here, quantitative measures were developed to account for the distribution of the four types of perceptual responses to 384 different stimuli from four talkers. The measures included mutual information, correlations, and acoustic measures, all representing audiovisual stimulus relationships. In Experiment 1, open-set perceptual responses were obtained for acoustic /bɑ/ or /lɑ/ dubbed to video /bɑ, dɑ, gɑ, vɑ, zɑ, lɑ, wɑ, eɑ/. The talker, the video syllable, and the acoustic syllable significantly influenced the type of response. In Experiment 2, the best predictors of response category proportions were a subset of the physical stimulus measures, with the variance accounted for in the perceptual response category proportions between 17% and 52%. That audiovisual stimulus relationships can account for perceptual response distributions supports the possibility that internal representations are based on modality-specific stimulus relationships.     

Evidence for phonetic processing of cues to place of articulation: Perceived manner affects perceived place

Using stimuli that could be labeled either as stops [b,d] or as fricatives [f,v,θ,ð], we found that, for a given acoustic stimulus, perceived place of articulation was dependent on perceived manner. This effect appeared for modified natural syllables with a free-identification task and for a synthetic transition continuum with a forced-choice identification task. Since perceived place could be changed by changing manner labels with no change in the acoustic stimulus, it follows that the processing of the place feature depends on the value the listener assigns to the manner feature rather than directly on any of the acoustic cues to manner. We interpret these results as evidence that the identification of place of articulation involves phonetic processing and could not be purely auditor     

The role of spectral and dynamic cues in imagery for musical timbre.

The musical quality of timbre is based on both spectral and dynamic acoustic cues. Four 2-part experiments examined whether these properties are represented in the mental image of a musical timbre. Experiment 1 established that imagery occurs for timbre variations within a single musical instrument, using plucked and bowed tones from a cello. Experiments 2 and 3 used synthetic stimuli that varied in either spectral or dynamic properties only, to investigate imagery with strict acoustic control over the stimuli. Experiment 4 explored whether the dimension of loudness is stored in an auditory image. Spectral properties appear to play a much larger role than dynamic properties in imagery for musical timbre.     

Use of vocalic cues to consonant voicing and native language background: The influence of experimental design

For native speakers of English and several other languages, preceding vocalic duration andFi offset frequency are two of the cues that convey the stop consonant voicing distinction in wordfinal position. For speakers learning English as a second language, there are indications that use of vocalic duration, but notFl offset frequency, may be hindered by a lack of experience with phonemic (i.e., lexical) vowel length (the “phonemic vowel length account”: Crowther & Mann, 1992). In this study, native speakers of Arabic, a language that includes a phonemic vowel length distinction, were tested for their use of vocalic duration andF1 offset in production and perception of the English consonant-vowel-consonant forms pod and pot. The phonemic vowel length hypothesis predicts that Arabic speakers should use vocalic duration extensively in production and perception. On the contrary, experiment l repealed that, consistent with Flege and Port’s (1981) findings, they produced only slightly (but significantly) longer vocalic segments in their pod tokens. It further indicated that their productions showed a significant variation inFl offset as a function of final stop voicing. Perceptual sensitivity to vocalic duration andFl offset as voicing cues was tested in two experiments. In experiment 2, we employed a factorial combination of these two cues and a finely spaced vocalic duration continuum. Arabic speakers did not appear to be very sensitive to vocalic duration, but they were abort as sensitive as native English speakers toF1 offset frequency. In Experiment 3, we employed a one-dimensional continuum of more widely spaced stimuli that varied only vocalic duration. Arabic speakers showed native-English-like sensitivity to vocalic duration- Anexplanation based on tie perceptual anchor theory of context coding (Braida et al., 1984; Macmillan, 1987; Macmillan, Braida, & Goldberg, 1987) and phoneme perception theory (Schouten & Van Hessen, 2992) is offered to reconcile the apparently contradictory perceptual findings. The explanation does not attribute native-English-like voicing perception to the Ambit subjects. The findings in this study call fox a modification of the phonemic vowel length hypothesis.     

Adaptation of speech by nonspeech: evidence for complex acoustic cue detectors

Three selective adaptation experiments were run, using nonspeech stimuli (music and noise) to adapt speech continua ([ba]-[wa] and [cha]-[sha]). The adaptors caused significant phoneme boundary shifts on the speech continua only when they matched in periodicity: Music stimuli adapted [ba]-[wa], whereas noise stimuli adapted [cha]-[sha]. However, such effects occurred even when the adaptors and test continua did not match in other simple acoustic cues (rise time or consonant duration). Spectral overlap of adaptors and test items was also found to be unnecessary for adaptation. The data support the existence of auditory processors sensitive to complex acoustic cues, as well as units that respond to more abstract properties. The latter are probably at a level previously thought to be phonetic. Asymmetrical adaptation was observed, arguing against an opponent-process arrangement of these units. A two-level acoustic model of the speech perception process is offered to account for the data.     

Consonant/vowel ratio as a cue for voicing in English

Several experiments investigate voicing judgments in minimal pairs likerabid-rapid when the duration of the first vowel and the medial stop are varied factorially and other cues for voicing remain ambiguous. In Experiments 1 and 2, in which synthetic labial and velar-stop voicing pairs are investigated, the perceptual boundary along a continuum of silent consonant durations varies in constant proportion to increases in the duration of the preceding vocalic interval. In Experiment 3, it is shown that speaking tempo external to the test word has far smaller effects on a closure duration boundary for voicing than does the tempo within the test word. Experiment 4 shows that, even within the word, it is primarily the preceding vowel that accounts for changes in the consonant duration effects. Furthermore, in Experiments 3 and 4, the effects of timing outside the vowel-consonant interval are independent of the duration of that interval itself. These findings suggest that consonant/vowel ratio serves as a primary acoustic cue for English voicing in syllable-final position and imply that this ratio possibly is directly extracted from the speech signal.     

Perceptual equivalence of acoustic cues in speech and nonspeech perception

Trading relations show that diverse acoustic consequences of minimal contrasts in speech are equivalent in perception of phonetic categories. This perceptual equivalence received stronger support from a recent finding that discrimination was differentially affected by the phonetic cooperation or conflict between two cues for the /slIt/-/splIt/contrast. Experiment 1 extended the trading relations and perceptual equivalence findings to the /sei/-/stei/contrast. With a more sensitive discrimination test, Experiment 2 found that cue equivalence is a characteristic of perceptual sensitivity to phonetic information. Using “sine-wave analogues” of the /sei/-/stei/stimuli, Experiment 3 showed that perceptual integration of the cues was phonetic, not psychoacoustic, in origin. Only subjects who perceived the sine-wave stimuli as “say” and “stay” showed a trading relation and perceptual equivalence; subjects who perceived them as nonspeech failed to integrate the two dimensions perceptually. Moreover, the pattern of differences between obtained and predicted discrimination was quite similar across the first two experiments and the “say”-“stay” group of Experiment 3, and suggested that phonetic perception was responsible even for better-than-predicted performance by these groups. Trading relations between speech cues, and the perceptual equivalence that underlies them, thus appear to derive specifically from perception of phonetic information.     

Some perceptual properties of consonants in multitalker babble

This study investigated whether consonant phonetic features or consonant acoustic properties more appropriately describe perceptual confusions among speech stimuli in multitalker babble backgrounds. Ten normal-hearing subjects identified 19 consonants, each paired with /a/, 1–19 and lui in a CV format. The stimuli were presented in quiet and in three levels of babble. Multidimensional scaling analyses of the confusion data retrieved stimulus dimensions corresponding to consonant acoustic parameters. The acoustic dimensions identified were: periodicity/burst onset, friction duration, consonant-vowel ratio, second formant transition slope, and first formant transition onset. These findings are comparable to previous reports of acoustic effects observed in white-noise conditions, and support the theory that acoustic characteristics are the relevant perceptual properties of speech in noise conditions. Perceptual effects of vowel context and level of the babble also were observed. These condition effects contrast with those previously reported for white-noise interference, and are attributed to direct masking of the low-frequency acoustic cues in the nonsense syllables by the low-frequency spectrum of the babble.     

Perceptual coherence of speech: stability of silence-cued stop consonants

A series of experiments was conducted to examine the perceptual stability of stop consonants cued by silence alone, as when [s] + silence + [laet] is perceived as splat. Following a replication of this perceptual integration phenomenon (Experiment 1), attempts were made to block it by instructing subjects to disregard the initial [s] and to focus instead on the onset of the following signal, which was varied from [plaet] to [laet]. However, these instructions had little effect at short silence durations (Experiment 2), and they reduced stop percepts for only 2 subjects at longer silence durations (Experiment 3). That is, subjects were generally unable to voluntarily dissociate the [s] noise from the following signal and thus to perceive the silent interval as silence rather than as a carrier of phonetic information. A low-uncertainty paradigm facilitated the task somewhat (Experiment 4). However, when the [s] frication was replaced with broadband noise (Experiment 5), listeners had no trouble at all in the selective-attention task, except at very short silence durations (less than 40 ms). This last finding suggests that, except for the shortest durations, the effect of silence on phonetic perception does not arise at the level of psychoacoustic stimulus interactions. Rather, the results support the hypothesis that perceptual integration of speech components, including silence, is a largely obligatory perceptual function driven by the listener's tacit knowledge of phonetic regularities.     

Trading relations in the perception of speech by 5-year-old children

Five-year-old children were tested for perceptual trading relations between a temporal cue (silence duration) and a spectral cue (F₁ onset frequency) for the “say-stay” distinction. Identification functions were obtained for two synthetic “say-stay” continua, each containing systematic variations in the amount of silence following the /s/ noise. In one continuum, the vocalic portion had a lower F₁ onset than in the other continuum. Children showed a smaller trading relation than has been found with adults. They did not differ from adults, however, in their perception of an “ay-day” continuum formed by varying F₁ onset frequency only. The results of a discrimination task in which the two acoustic cues were made to “cooperate” or “conflict” phonetically supported the notion of perceptual equivalence of the temporal and spectral cues along a single phonetic dimension. The results indicate that young children, like adults, perceptually integrate multiple cues to a speech contrast in a phonetically relevant manner, but that they may not give the same perceptual weights to the various cues as do adults.     

Impairment of auditory perception and language comprehension in dysphasia

Men with chronic focal brain wounds were examined for their ability to discriminate complex tones, synthesized steady-state vowels, and synthesized consonant—vowel syllables. Subjects with left hemisphere damage, but not right hemisphere damage, were impaired in their ability to respond correctly to rapidly changing acoustic stimuli, regardless of whether stimuli were verbal or nonverbal. The degree of impairment in auditory processing correlated highly with the degree of language comprehension impairment. The pattern of impairment of the group with left hemisphere damage on these perceptual tests was similar to that found in children with developmental language disorders.     

Auditory and linguistic processing of cues for place of articulation by infants

Two- and 3-month-old infants were found to discriminate the acoustic cues for the phonetic feature of place of articulation in a categorical manner; that is, evidence for the discriminability of two synthetic speech patterns was present only when the stimuli signaled a change in the phonetic feature of place. No evidence of discriminability was found when two stimuli, separated by the same acoustic difference, signaled acoustic variations of the same phonetic feature. Discrimination of the same acoustic cues in a nonspeech context was found, in contrast, to be noncategorical or continuous. The results were discussed in terms of infants’ ability to process acoustic events in either an auditory or a linguistic mode.     

Measuring the difference limen for identification of order of onset for complex auditory stimuli

The approximately 20-msec perceptual threshold for identifying order of onset for components of auditory stimuli has been considered both as a possible factor contributing to the perception of voicing contrasts in speech and as no more than a methodological artifact. In the present research, we investigate the identification of the temporal order of onset of spectral components in terms of the first of a sequence of thresholds for complex stimuli (modeled after consonant-vowel [CV] syllables) that vary in degree of onset. The results provide clear evidence that the difference limen (DL) for discriminating differences in onset time follows predictions based on a fixed perceptual threshold or limit at relatively short onset differences. Furthermore, the DL seems to be a function of context coding of stimulus information, with both the DL and absolute threshold probably reflecting limits on the effective perception and coding of the short-term stimulus spectrum.     

Duplex perception of cues for stop consonants: Evidence for a phonetic mode

When the (vocalic) formant transitions appropriate for the stops in a synthetic approximation to [spa] or [sta] are presented to one ear and the remainder of the acoustic pattern to the other, listeners report a duplex percept. One side of the duplexity is the same coherent syllable ([spa] or [sta]) that is perceived when the pattern is presented in its original, undivided form; the other is a nonspeech chirp that corresponds to what the transitions sound like in isolation. This phenomenon is here used to determine why, in the case of stops, silence is an important cue. The results show that the silence cue affects the formant transitions differently when, on the one side of the duplex percept, the transitions support the perception of stop consonants, and when, on the other, they are perceived as nonspeech chirps. This indicates that the effectiveness of the silence cue is owing to distinctively phonetic (as against generally auditory) processes.